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CHAPTER 3. Density and measuring technique CHEMISTRY 1105
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Metals ► 90% of the elements on the Periodic Table are metals ► Physical properties define the metal ◦Weight ◦Mass ◦How about volume? ◦How about the phase of the metal? ► Melting Point ► Boiling Point
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Where are the metals in the P.T?
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We will determine the density of a metal!
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Density ◦A physical property ◦How heavy something is compared to its size. ◦Relationship between mass and volume
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But why? ◦Type of Molecules ◦Crystal structure ◦Interactions
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Remember
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Density of liquids If two liquids of different densities are poured together, they form tow layers: Top Liquid with lowest density Bottom Liquid with highest density
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Experiment
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Materials ? 50 & 100 mL 10 mL
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Density of a solid How will we do it? Measuring the displacement of H 2 0 2 1 Weigh the metal
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Procedure 1.Select you metal and record how it looks like. 2.Using the balance, get 3 different mass measurements of the metal ◦Small medium large (1 time each) ◦Then repeat two more times! ◦Total= 9 measurements ◦Do it for precision
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To determine the volume We know that an object will displace its own volume within another volume 3.Use a 10 mL graduated cylinder 4.Fill it with 5 mL of DI H 2 0, and get rid of bubbles. Record the exact initial volume (meniscus). 5.Place metal pieces into graduated cylinder (angle). 6.Get rid of bubbles and record the final volume.
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Repeat for each of the metal sizes Do it 3 times!
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Computer calculations The change in volume equals the volume displacement Volume of metal = Final volume – Initial volume 1.Login the computer 2.Open Excel 3.Blank workbook
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Spreadsh eet 4.Fill the column names ◦Column A: Size ◦Column B: Trial ◦Column C: Mass ◦Column D: Initial volume ◦Column E: Final volume ◦Column F: Displaced volume 5.Fill the first row information ◦1 to 3: Small ◦4 to 6: Medium ◦7 to 9: Large 6.Fill the second row information ◦1, 2, 3 (three times)
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7.Fill in the data from your experiment 8.Calculate the volume displaced by your metal. ◦Use an excel formula ◦Pull the box all the way down to copy the formula Analysis & Graph
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9.Hide columns D and E Analysis & Graph
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10.Select mass and volume values 11.Insert graph ◦Scatter 12.Fill the graph with your information: X axis: Volume (mL) Y axis: Mass (g) Title: Density of (describe) metal Analysis & Graph
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13. Select one of the dots ◦Right click ◦Add trendline ◦Linear ◦Display equation on chart Analysis & Graph
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y = m*x + b m –slope which relates accuracy b –intercept which is the density
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Find the unknown! ◦Chemistry book ◦Periodic table ◦Write it in your report
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Print one copy of the Excel sheet per group member
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Density of a liquid How will we do it? Measuring the mass of the liquid and the volume it occupies 21 Weigh the liquid Record the volume of liquid
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Procedure 1.Use a 100 mL beaker and get 50 mL of the unknown liquid 2.Rinse the pipette with 5 mL of liquid and discard it 3.Clean and dry a 50 mL beaker and weight it empty. Record this mass waste
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4.Pipette 3 to 6 mL of liquid ◦Record the exact volume 5.Pour the liquid in the beaker and record the mass (do not subtract the mass of the beaker) Repeat the process 8 more times, but leaving the previous liquid in the beaker
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Calculations Repeat the same procedure in Excel Open a second sheet
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y = m*x + b b –the weight of the beaker m –slope which is the density
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Find the unknown! ◦Chemistry book ◦Write it in your report
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Print one copy of each sheet per group member
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Report ◦Print graph and table ◦Staple graph and report together ◦Don’t forget to describe and name your unknown! ◦Staple all lab reports together ◦Clean everything before leaving and place it back in its place.
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